INDIANAPOLIS—A long-awaited engineering report into last year's fatal stage collapse at the Indiana State Fair concludes the collapse occurred when concrete Jersey barriers attached to guy wires meant to provide lateral support to the stage system began to slide as wind speeds increased during a severe storm.

“From a technical standpoint, the structure did not have adequate lateral capacity,” said Scott Nacheman, vp at Thornton Tomasetti Inc. in Chicago. “The Jersey barriers slid and that caused the system to fail.”

Absent the lateral support that the Jersey barrier and guy wire system was meant to provide, “Once gravity had essentially taken over, there was no way for the structure to support itself,” Mr. Nacheman said.

The Thornton Tomasetti report and another examining the Aug. 13, 2011, event produced by emergency preparedness firm Witt Associates, were released by the Indiana State Fair Commission on Thursday, with representatives of the firms presenting summaries of their findings to a meeting of the commission's board.

The collapse of the stage roof and scaffolding before a performance of the country duo Sugarland killed seven and injured 58.

Mr. Nacheman said the engineering study found that while wind speeds at the fairgrounds reached a maximum of 59 mph during the storm, by code prescribed standards the stage system should have been able to resist winds of 68 mph. “The system was found to fail at wind speeds lower than code and standard provisions,” he said.

And, Mr. Nacheman said, Thornton Tomasetti's review found that even if the guy line and ballast system had provided sufficient strength to resist the wind loads, other components of the system did not have sufficient strength and would have failed if the Jersey barriers hadn't moved first.

Among Thornton Tomasetti's recommendations was that in the future such outdoor stages should be designed by licensed design professionals, and additional reviews should be conducted if performers seek to hang equipment on the stage structure not anticipated in the original design.

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“These all need to be designed and permitted as Class 1 structures,” Mr. Nacheman said. “We feel that that design should be submitted for a permit as any Class 1 structure should be. That permit should be reviewed by a competent reviewer.”

After the structures are built, they should be reviewed by a design professional to confirm that the original design was implemented properly, he said.

Referring to the Jersey barrier and guy wire system used on the state fair stage, Mr. Nacheman said, “We strongly disagree with the use of moveable ballast for temporary entertainment structures.”

In summarizing the Witt Associates report, Charles Fisher and Kenneth Mallette, both vps with the Washington-based firm, offered a picture of a lack of defined emergency decision-making and information-sharing procedures at the time of the stage collapse.

In detailing a timeline of the event, Mr. Mallette noted that Cynthia Hoye, the state fair commission's executive director, and Capt. Brad Weaver of the Indiana State Police were on their way to the stage to announce an evacuation when the collapse occurred.

Witt Associates found that while the state fair commission had taken some emergency preparedness steps prior to the stage collapse, “the overall state of preparedness was not appropriate for an event of the size and scope of the Indiana State Fair,” Mr. Fisher said. “What we found was, though they did have plans in place, the emergency response plans were not fully developed.”

Mr. Fisher said Witt Associates' report contains approximately 80 recommendations, including that the state fair commission develop a comprehensive emergency preparedness plan; that it develop formal protocols for delaying or canceling productions with one person charged with responsibility for the decision; and that the commission create a public safety position, with that individual reporting directly to the commission's executive director.